A bit like an RFID tag, a passkey is a piece of electronics about the size of a grain of rice, surgically implanted, usually somewhere in the abdomen.
Like an RFID tag, a passkey will respond to the right coded signal with information about its owner. Unlike an RFID tag, the passkey contains deeply-encrypted biometric data and security clearance codes.
The "Big Brother" side of the technology involves pervasive logging of people's movements. Passkeys are routinely scanned in towns and major sites of interest. Mostly, these are just passive records of identities as people pass nearby.
The benefit to the wearer, at least those high up in the hierarchy, is that their identity is automatically verified, giving them access to facilities so seamlessly that they are rarely even aware of the rings of security they've passed through. These kinds of checks involve more than passive logging. Access codes will be checked against clearance levels, and the monitoring station may verify biometric details.
The Empire places great faith in the security of its passkey technology. It uses signaling and encryption technology far removed from the general interchange standards used throughout civilization.
The Empire knew nothing about Shayla's brother, Brandt.
Naturally, posing as a high-ranking public servant, Shayla needed her own passkey.
Nobody outside of the Imperial Security Services laboratories has ever been able to forge a passkey good enough to fool the strict checks used around the Imperial capital. Brandt was no exception in this respect.
Shayla bypassed the problem of forgery by stealing one, after making sure its previous owner had no further need of it, of course.
With a genuine piece of technology in his hands, Brandt was able to crack the security, allowing Shayla to encrypt her own biometrics and any chosen set of access codes into the device. All she needed to do was read off and decrypt the access codes and identity information from her chosen target.